The present invention relates to the technical field of a display device, and particularly to the technical field of a display device such as a liquid crystal display device or the like which can be used as both a reflective display type utilizing reflection of external light and a transmissive type utilizing transmission of light from a light source, and an electronic apparatus using the display device, such as a portable telephone, a watch, or the like.
In a conventional reflective display device performing display by using external light, display is made hard to see in dark in accordance with decreases in the quantity of light. On the other hand, in a transmissive display device performing display by using a light source such as a back light or the like, the power consumption is increased by the amount corresponding to the light source regardless of the brightness of place, and particularly it is unsuitable as a portable display device operated by a battery. Therefore, in a transflective display device which can be used as both the reflective and transmissive display devices, mainly in the light, light being incident from the display screen is reflected by a semi-reflecting film provided in the device, and at the same time, the quantity of light emitted from the display screen is controlled for each pixel by using a liquid crystal, an optical element such as a polarized light separator or the like, which are arranged on the optical path, to perform reflective display. On the other hand, mainly in the dark, from the back of the semi-reflecting film, the light is irradiated from the light source, and at the same time, the quantity of light emitted from the display screen is controlled for each pixel by using the above mentioned liquid crystal, the optical element such as a polarized light separator or the like to perform transmissive display.
In a conventional liquid crystal display device utilizing a variable transmission polarization axis optical element making the polarization axis of transmitted light to be rotated, such as a TN (Twisted Nematic) liquid crystal, a STN (Super-Twisted Nematic) liquid crystal or the like, a structure is employed in which the variable transmission polarization axis optical element is held between two polarizers. A polarizer as an example of polarized light separators polarizes incident light by absorbing a polarized light component in a direction different from the polarization axis in a predetermined direction, and thus exhibits poor efficiency of light utilization. Particularly, in the above liquid crystal display device which can be used as both the reflective and transmissive display devices, in reflective display, light is reflected by the semi-reflecting film, thereby further deteriorating the efficiency of light utilization. Therefore, there is the problem of dark display in reflective display.
A conventional transflective display device using a TN liquid crystal panel as variable transmission polarization axis means is described with reference to FIG. 31. FIG. 31 is a sectional view of a conventional transflective display device.
In FIG. 31, the display device comprises an upper polarizer 5130, a TN liquid crystal panel 5140, a lower polarizer 5170, a transflector 5180, and a light source 5210. Although, in FIG. 31, the respective portions are shown as separate portions for the sake of clarity, the portions are, in fact, closely arranged. The upper polarizer 5130 and the lower polarizer 5170 are arranged so that the transmission polarization axes thereof are perpendicular to each other in order to perform normally white display.
White display in reflective display is described. The light shown on the optical path 5111 is changed to linearly-polarized light parallel to the drawing by the upper polarizer 5130, and the polarization axis is twisted for 90xc2x0 by the TN liquid crystal panel 5140 to produce linearly-polarized light perpendicular to the drawing. The linearly-polarized light is transmitted through the lower polarizer 5170 keeping perpendicular to the drawing, and reflected by the transflector 5180, with a part transmitted. The reflected light is again transmitted as linearly-polarized light perpendicular to the drawing through the lower polarizer 5170, and the polarization axis is twisted for 90xc2x0 by the TN liquid crystal panel 5140 to produce linearly-polarized light parallel to the drawing, which is then emitted from the upper polarizer 5130.
Since each of the upper polarizer 5130 and the lower polarizer 5170 is a polarized light separator accompanied with absorption respectively, a part of light is absorbed during the transmissions through the upper polarizer 5130 and the lower polarizer 5170 twice for each. Furthermore, some light is transmitted through the transflector 5180 and travels toward the light source 5210, and is not used for display. As a result, the conventional transflective liquid crystal display device exhibits a low efficiency of light utilization, and thus has the problem of darkening the display screen, particularly, in reflective display.
Therefore, the inventors proposed a transflective display device described in Japanese Patent Application No. 8-245346, which had not been published, as yet, on the priority date of this application, in which the lower polarizer and the transflector, which are on the light source side, are substituted with a reflective polarizer, which is an example of polarized light separators to reflect the light of a linearly-polarized component in a predetermined direction and also to transmit the light of a linearly-polarized component being in the direction perpendicular to the predetermined direction. In this display device, the efficiency of reflection is increased by the polarized light separator to obtain bright display. Also a display device using a reflective polarizer is disclosed in the Published Japanese Translations of PCT International Publication for Patent applications No. 9-506985 (International Publication No. WO/95/17692) and International Publication No. WO/95/27819).
Description will now be made on the transflective display device using the reflective polarizer proposed by the inventors in Japanese Patent Application No. 8-245346, with reference to FIG. 32.
In FIG. 32, the display device comprises the upper polarizer 5130, an upper glass substrate 5302, a lower glass substrate 5304, a polarized light separator 5160, a transflective light absorption film 5307, and the light source 5210. The display device further comprises a TN liquid crystal panel held between the upper glass substrate 5302 and the lower glass substrate 5304, the TN liquid crystal panel includes a voltage applied region 5110 and a voltage unapplied region 5120. Particularly, the polarized light separator 5160 comprises a reflective polarizer.
First, white and black display in reflective display is described. The light, which is shown on the optical path 5601 and is incident from the outside of the display device, is changed to linearly-polarized light parallel to the drawing by the upper polarizer 5130, and then, the polarization direction of it is twisted for 90xc2x0 by the voltage unapplied region 5120 of the TN liquid crystal panel to produce light of a linearly-polarized component being in the direction perpendicular to the drawing. After that the light is reflected by the polarized light separator 5160 as it is a linearly-polarized component light perpendicular to the drawing, and then the polarization direction is twisted for 90xc2x0 by the TN liquid crystal panel to produce light of a linearly-polarized component parallel to the drawing, which is then emitted from the upper polarizer 5130. Therefore, with no voltage applied to the TN liquid crystal panel, white display is obtained. In this way, the light of white display is the light reflected by the polarized light separator 5160 which selectively reflects most of the linearly-polarized light transmitted through the upper polarizer 5130, thereby obtaining brighter display than the conventional display device (refer to FIG. 31) using the transflector for simply partly reflecting the light transmitted through the polarizer. The light shown on the optical path 5603 is changed to linearly-polarized light parallel to the drawing by the upper polarizer 5130, then transmitted as linearly-polarized light parallel to the drawing through the voltage applied region 5110 of the TN liquid crystal panel without a change in the polarization direction, and further transmitted through the polarized light separator 5160 without a change in the polarization direction, and then absorbed by the transflective light absorbing layer 5307 to produce black display.
On the other hand, in transmissive display, the light from the light source 5210, which is shown on the optical path 5602, is transmitted through the opening provided in the transflective light absorbing layer 5307 and changed to linearly-polarized light parallel to the drawing by the polarized light separator 5160 (namely, the polarized component being in the direction perpendicular to the drawing is reflected by the lower side of the polarized light separator 5160 and absorbed by the transflective light absorbing layer 5307). Then the polarization direction is twisted for 90xc2x0 by the voltage unapplied region 5120 of the TN liquid crystal panel to produce linearly-polarized light perpendicular to the drawing, which is absorbed by the upper polarizer 5130 to obtain black display. The light on the optical path 5604 is transmitted through the opening provided in the transflective light absorbing layer 5307, and changed to linearly-polarized light parallel to the drawing by the polarized light separator 5160, and then transmitted as linearly-polarized light parallel to the drawing through the upper polarizer 5130 without a change in the polarization direction at the voltage applied region 5110 of the TN liquid crystal panel to obtain white display.
In this way, the transflective display device using a reflective polarizer as a polarized light separator, which was proposed by the inventors in Japanese Patent Application No. 8-245346, is capable of performing reflective display using external light in the bright place, and transmissive display using the light from a light source in the dark place.
However, as described above with reference to FIG. 32, in the transflective display device using the reflective polarizer as a polarized light separator, light reflected by the reflective polarizer is used for display in transmissive display, while light transmitted through the reflective polarizer is used for display in reflective display. Therefore, in transmissive display, a portion where a voltage is applied to the liquid crystal panel (the polarization direction is not twisted by the TN liquid crystal) produces white display, i.e., negative display is performed. In reflective display, a portion where a voltage is not applied to the liquid crystal panel (the polarization direction is twisted for 90xc2x0 by the TN liquid crystal) produces white display, i.e., positive display is performed. Namely, in reflective display, a display, in which white and black are the reverse of the display in transmissive display, is performed. In this way, the display device proposed by the inventors in Japanese Patent Application No. 8-245346 has the problem of causing so-called xe2x80x9cpositive-negative reversalxe2x80x9d between transmissive display and reflective display.
The present invention has been achieved for solving the above problem, and an object of the present invention is to provide a display device using a variable transmission polarization axis optical element such as a liquid crystal or the like, causing no positive-negative reversal both in reflective display using external light and transmissive display using the light from a light source, and capable of producing bright display, and also to provide an electronic apparatus using the display device.
The above objects of the present invention can be achieved by a display device comprising variable transmission polarization axis means capable of changing the transmission polarization axis, first polarized light separating means arranged on the one side of the variable transmission polarization axis means, for transmitting light of a linearly-polarized component in a first direction and for reflecting light of a linearly-polarized light component in a predetermined direction different from the first direction, second polarized light separating means arranged on the other side of the variable transmission polarization axis means for transmitting light of a linearly-polarized component in a second direction and for reflecting or absorbing light of a linearly-polarized component in a predetermined direction different from the second direction, and light source means for making light to be incident from between the first and second polarized light separating means.
According to this display device, on the one side of the variable transmission polarization axis means, the first polarized light separating means transmits a linearly-polarized light component in the first predetermined direction, out of the light being incident from the variable transmission polarization axis means side, to the side opposite to the variable transmission polarization axis means side, and reflects a linearly-polarized light component being in the predetermined direction (for example, perpendicular or substantially perpendicular to the first direction) different from the first predetermined direction to the variable transmission polarization axis means side. On the other side of the variable transmission polarization axis means, the second polarized light separating means transmits a linearly-polarized light component being in the second predetermined direction, out of the light being incident from the variable transmission polarization axis means, to the side opposite to the variable transmission polarization axis means side, and reflects to the variable transmission polarization axis means side or absorbs a linearly-polarized light component being in the predetermined direction (for example, perpendicular or substantially perpendicular to the second direction) different from the second predetermined direction.
In this way, the first polarized light separating means transmits a linearly-polarized light component being in the first direction being incident from the variable transmission polarization axis means side, and reflects a linearly-polarized light component different from the first linearly-polarized light component in order to perform the separation of the polarized light. Therefore, this display device can obtain brighter display because it utilizes the reflected linearly-polarized light, as compared with a conventional display device using a polarizer which performs the separation of the polarized light by transmitting a linearly-polarized light component in a certain direction and absorbs the other linearly-polarized light component being in the direction perpendicular to the aforementioned one linearly-polarized light component.
Furthermore, in this display device, since light is incident between the first polarized light separating means and the second polarized light separating means from the light source means, it means that the light is incident from the upper side relative to the first polarized light separating means. Namely, like in the case of external light in reflective display, the light from the light source is made to be incident to the first polarized light separating means from the upper side. Therefore, unlike in the display device proposed by the inventors in Japanese Patent Application No. 8-245346, the light from the light source of the subject display device is not incident from the lower side, thereby causing no negative-positive reversal. Also freedom of the arrangement position of the light source is increased to increase design freedom of the display device.
In the display device in accordance with an embodiment of the present invention, the first polarized light separating means comprises a reflective polarizer which transmits light of a linearly-polarized light component being in the first direction, and reflects light of a linearly-polarized light component being in the direction perpendicular to the first direction.
In this embodiment, the reflective polarizer transmits the linearly-polarized light component, out of the light being incident from the variable transmission polarization axis means side, which is in the first predetermined direction as a linearly-polarized light component, which is in the first predetermined direction, to the side opposite to the variable transmission polarization axis means side, and reflects the linearly-polarized light component which is in the direction perpendicular to the first predetermined direction as a linearly-polarized light component, which is in the direction perpendicular to the first predetermined direction, to the variable transmission polarization axis means side. Also, out of the light being incident from the side opposite to the variable transmission polarization axis means side, the linearly-polarized light component being in the first predetermined direction is transmitted as a linearly-polarized light component being in the first predetermined direction, to the variable transmission polarization axis means side, the linearly-polarized light component being in the direction perpendicular to the first predetermined direction is reflected as a linearly-polarized light component being in the direction perpendicular to the first predetermined direction, to the side opposite to the variable transmission polarization axis means side.
Furthermore, in this embodiment, the reflective polarizer may comprise a laminate in which a first layer having birefringence and a second layer having a refractive index substantially equal to any one of the plurality of refractive indexes of the first layer, and no birefringence are alternately laminated.
In the reflective polarizer having the above construction, out of the light being incident on one of the main surface of the reflective polarizer from the lamination direction, the light of a linearly-polarized component being in the first direction is transmitted as a linearly-polarized light component being in the first direction to the other main surface side located on the opposite side, and the linearly-polarized light component being in the direction perpendicular to the first direction is reflected as a linearly-polarized light component being in the direction perpendicular to the first direction. While, out of the light being incident on the other main surface of the reflective polarizer from the lamination direction, the linearly-polarized light component being in the first direction is transmitted as a linearly-polarized light component being in the first direction to the one main surface side, located on the opposite side, and the linearly-polarized light component being in the direction perpendicular to the first direction is reflected as a linearly-polarized light component being in the direction perpendicular to the first direction.
In a display device in accordance with another embodiment of the present invention, the second polarized light separating means comprises a reflective polarizer which transmits a linearly-polarized light component being in the second direction and reflects a linearly-polarized light component being in the direction perpendicular to the second direction.
In this embodiment, the reflective polarizer reflects the linearly-polarized light component being in the second predetermined direction, out of the light being incident from the variable transmission polarization axis means side, as a linearly-polarized light component being in the second predetermined direction to the side opposite to the variable transmission polarization axis means side, and reflects the linearly-polarized light component being in the direction perpendicular to the second predetermined direction as a linearly-polarized light component being in the direction perpendicular to the second direction to the variable transmission polarization axis means side. Also, out of the light being incident from the side opposite to the variable transmission polarization axis means side, the linearly-polarized light component being in the second predetermined direction is transmitted as a linearly-polarized light component being in the second predetermined direction to the variable transmission polarization axis means side, and the linearly-polarized light component being in the direction perpendicular to the second predetermined direction is reflected as a linearly-polarized light component being in the direction perpendicular to the second predetermined direction to the side opposite to the variable transmission polarization axis means side.
Therefore, out of the light emitted from the light source, the linearly-polarized light component being in the second predetermined direction is transmitted to the side opposite to the variable transmission polarization axis means side, and further the linearly-polarized light component being in the direction perpendicular to the second predetermined direction is partially repeatedly reflected in the display device, and finally passed through the reflective polarizer and emitted to the side opposite to the variable transmission polarization axis means side. Therefore, when display is performed by using the light from the light source, the brighter display can be obtained as compared with the case using the polarizer as the second polarized light separating means.
Furthermore, in this embodiment, the reflective polarizer may comprise a laminate in which a first layer having birefringence and a second layer having a refractive index substantially equal to any one of the plurality of refractive indexes of the first layer, and no birefringence are alternately laminated.
In the reflective polarizer having the above construction, out of the light being incident on a main surface of the reflective polarizer from the lamination direction, light of a linearly-polarized component being in the second direction is transmitted as a linearly-polarized light component being in the second direction to the other main surface side on the opposite side, and the linearly-polarized light component being in the direction perpendicular to the second direction is reflected as a linearly-polarized light component being in the direction perpendicular to the second direction. While, out of the light being incident on the other main surface of the reflective polarizer from the lamination direction, the linearly-polarized light component being in the second direction is transmitted as a linearly-polarized light component being in the second direction to the one main surface located on the opposite side, and the linearly-polarized light component being in the direction perpendicular to the second direction is reflected as a linearly-polarized light component being in the direction perpendicular to the second direction.
In a display device in accordance with still another embodiment of the present invention, the second polarized light separating means comprises a polarizer which transmits a linearly-polarized light component being in the second direction and absorbs a linearly-polarized light component being in the direction perpendicular to the second direction.
In the polarizer of this embodiment, out of the light being incident from the variable transmission polarization axis means side, the linearly-polarized light component being in the second predetermined direction is transmitted as a linearly-polarized light component being in the second predetermined direction to the side opposite to the variable transmission polarization axis means side, and the linearly-polarized light component being in the direction perpendicular to the second predetermined direction is absorbed. Also, out of the light being incident from the side opposite to the variable transmission polarization axis means side, the linearly-polarized light component being in the second predetermined direction is transmitted as a linearly-polarized light component being in the second predetermined direction to the variable transmission polarization axis means side, and the linearly-polarized light component being in the direction perpendicular to the second predetermined direction is absorbed.
A display device in accordance with a further embodiment of the present invention further comprises an optical element arranged on the side opposite to the variable transmission polarization axis means side with respect to the first polarized light separating means so that of the light from the first polarized light separating means, light in a predetermined wavelength region is emitted to the first polarized light separating means.
In this embodiment, in observation of the display device from the second polarized light separating means side, for the light, which is incident between the first polarized light separating means and the second polarized light separating means from the light source means, two display states, namely, the first display state due to the light reflected by the first polarized light separating means and the second display state due to the light, which is emitted from the optical element with predetermined wavelength region and transmitted through the first polarized light separating means, are obtained depending on the conditions of the transmission polarization axis of the variable transmission polarization axis means. Since, the first display state is a display state due to the light reflected from the first polarized light separating means, bright display can be obtained.
On the other hand, for external light from the outside of the second polarized light separating means, two display states namely, the third display state due to light reflected by the first polarized light separating means and the fourth display state due to light, which is emitted from the optical element with the predetermined wavelength region and transmitted through the first polarized light separating means, are obtained depending on the condition of transmission polarization axis of the variable transmission polarization axis means. Since, the third display state is a display state due to the light reflected from the first polarized light separating means, bright display can be obtained.
Furthermore, the two display states (bright and dark), which are obtained depending on the conditions of transmission polarization axis of the variable transmission polarization axis means are the same in either case of the display utilizing the eternal light and the display utilizing the light from the light source. Namely, when the transmission polarization axis of the variable transmission polarization axis means is in the first state, if the display due to the light being incident from the outside of the second polarized light separating means is bright, the display due to the light from the light source is also bright. When the transmission polarization axis of the variable transmission polarization axis means is in the second state, if the display due to light being incident from the outside of the second polarized light separating means is dark, the display due to the light from the light source is also dark. Therefore, there is no problem of the positive-negative reversal between the display due to light being incident from the outside of the second polarized light separating means and the display due to the light emitted from the light source.
In this embodiment, the optical element may comprise an optical element, which absorbs the light in the visible light region other than the predetermined wavelength region of light emitted from the first polarized light separating means, and is capable of partially reflecting the light in the predetermined wavelength region toward the first polarized light separating means and is also capable of partially transmitting the light in the predetermined wavelength region.
Further, in this case, the optical element may comprise a color filter. This construction enables color display according to the color of the color filter to be performed.
In this embodiment, the display device may further comprise reflection means arranged on the side opposite to the first polarized light separating means side with respect to the optical element so that at least light in the predetermined wavelength region can be reflected to the optical element.
Such reflection means can brighten the second or fourth display state due to the light emitted from the optical element.
According to the still further embodiment of the present invention, the display device further comprises an optical element arranged on the side opposite to the variable transmission polarization axis means side with respect to the first polarized light separating means so that the light in the visible light region out of the light in the visible light region is absorbed.
In this embodiment, the optical element may comprise a an light absorber in black color.
In this construction, in observation of the display device from the second polarized light separating means side, for the light which is incident between the first polarized light separating means and the second polarized light separating means from the light source, two display states namely, the fifth display state due to the light reflected by the first polarized light separating means and the sixth display state of black display are obtained depending on the conditions of the transmission polarization axis of the variable transmission polarization axis means. Since, the fifth display state is a display state due to the light reflected from the first polarized light separating means, bright display and high contrast to the sixth display state are obtained.
Also, for external light from the outside of the second polarized light separating means, two display states namely, the seventh display state due to the light reflected by the first polarized light separating means and the eighth display state of black display are obtained depending on the conditions of transmission polarization axis of the variable transmission polarization axis means. Since, the seventh display state is a display state due to the light reflected from the first polarized light separating means, bright display and high contrast to the eighth display state are obtained. Further, the display states, which are obtained depending on the conditions of transmission polarization axis of the variable transmission polarization axis means, are the same in either case of the display utilizing the light from the light source and in display utilizing external light, thereby causing no problem of the positive-negative reversal, which is aforementioned.
A display device in accordance with a further embodiment of the present invention further comprises a transmissive light diffusion layer provided between the first polarized light separating means and the variable transmission polarization axis means.
In this embodiment, display due to the light reflected from the first polarized light separating means is white. The light diffusion layer may be provided with a light guide function so as to be also used as a light guide plate which will be described below. Namely, in this case, the light diffusion layer has not only the function to diffuse light being incident from the upper side or lower side, but also the function to diffuse the light being incident from lateral sides to the vertical direction. Further, in this case, the quantity of light, which is emitted from the light diffusion layer to the first polarized light separating means side, is preferably larger than the quantity of light, which is emitted in the reverse direction. This is because the former contributes to the display contrast. The light diffusion layer may be arranged on one side or both sides of the light guide plate.
In this embodiment, the surface of the light diffusion layer may be an irregular surface or rough surface. This construction can relatively easily realize the light diffusion function.
Alternatively, in this embodiment, the light diffusion layer may contain particles having light diffusivity. This construction can relatively easily realize the light diffusion function.
In a display device in accordance with a further embodiment of the present invention, the light source means comprises a light source, and a transmissive light guide plate arranged between the second polarized light separating means and the variable transmission polarization axis means to guide the light from the light source to between the second polarized light separating means and the variable transmission polarization axis means, and emit the light at least to the variable transmission polarization axis means side.
In this embodiment, the light from the light source is guided by the light guide plate between the second polarized light separating means and the variable transmission polarization axis means, and emitted to at least the variable transmission polarization axis means side, and then reflected by the first polarized light separating means to be used for display. In this case, although it is also possible to make arrangement so as to make the light from the light source to be emitted to the second polarized light separating means side by the transmissive light guide plate, the light emitted to the variable transmission polarization axis means side contributes to the display contrast. The light being incident from the upper side or lower side of the light guide plate is transmitted through the transmissive light guide plate and thus does not interfere with the light used for display.
In this embodiment, the light source means may further comprise a light guide for guiding the light from the light source to the light guide plate. This construction increases freedom of the arrangement position of the light source, and further increases design freedom of the display device.
In this case, an end of the light guide may be located between the second polarized light separating means and the variable transmission polarization axis means, and the second polarized light separating means may be fixed to the light guide. This construction permits the light guide to be also used as a member for fixing the variable transmission polarization axis means and is thus advantageous.
Alternatively, in this case, the variable transmission polarization axis means may be fixed by the light guide. This construction permits the light guide to be also used as a member for fixing the variable transmission polarization axis means and is thus advantageous.
In the embodiment in which the light guide plate is provided between the second polarized light separating means and the variable transmission polarization axis means, the light guide plate may comprise a transmissive flat plate, and an irregular portion, which is formed on at least the variable transmission polarization axis means side of the flat plate and emits the light from the light source to the variable transmission polarization axis means side. This construction permits light emission through the uneven portion with relatively high efficiency.
In this case, the uneven portion may contain a plurality of projections discretely provided. This construction permits light emission through the sides of the plurality of projections with relatively high efficiency.
Furthermore, in this case, the projections may have a size of 5 to 300 xcexcm. With a size of 5 xcexcm or more, no influence of diffraction occurs, and with a size of 300 xcexcm or less, the visual interference of the projections can be eliminated.
In the embodiment in which the light guide plate is provided between the second polarized light separating means and the variable transmission polarization axis means, the light guide plate may exhibit substantially optical isotropy. With a light guide plate exhibiting optical anisotropy, the display appearance is colored, thereby causing color irregularity. With the light guide plate exhibiting substantially optical isotropy, neither coloring of the display appearance nor color irregularity occurs.
Alternatively, in the embodiment in which the light guide plate is provided between the second polarized light separating means and the variable transmission polarization axis means, the light guide plate may be optically uniaxial or biaxial. With such an optically uniaxial or biaxial light guide plate having optical anisotropy with regularity, no color irregularity occurs, and thus it is possible to widen the viewing angle of display and improve the contrast.
In a display device in accordance with a further embodiment of the present invention, the light source means comprises a light source and a transmissive light guide plate arranged between the first polarized light separating means and the variable transmission polarization axis means, for guiding the light from the light source between the first polarized light separating means and the variable transmission polarization axis means, as well as emitting the light to at least the first polarized light separating means side.
In this embodiment, the light from the light source is guided by the transmissive light guide plate between the first polarized light separating means and the variable transmission polarization axis means and emitted to at least the first polarized light separating means side, and then reflected by the first polarized light separating means to be used for display. In this case, although the light from the light source may be emitted to the variable transmission polarization axis means side by the transmissive light guide plate, the light emitted to the first polarized light separating means side contributes to the display contrast. The light being incident from the upper side or lower side of the light guide plate is transmitted through the transmissive light guide plate and thus does not interfere with the light used for display.
In this embodiment, the light source means may further comprise a light guide for guiding the light from the light source to the light guide plate. This construction increases freedom of the arrangement position of the light source, and further increases design freedom of the display device.
In this case, an end of the light guide may be located on the second polarized light separating means, and the second polarized light separating means may be fixed to the light guide. This construction permits the light guide to be also used as a member for fixing the second polarized light separating means and is thus advantageous.
Alternatively, in this case, the variable transmission polarization axis means may be fixed by the light guide. This construction permits the light guide to be also used as a member for fixing the variable transmission polarization axis means and is thus advantageous.
In the embodiment comprising the light guide plate provided between the first polarized light separating means and the variable transmission polarization axis means, the light guide plate may comprise a transmissive flat plate and an uneven portion formed on at least the first polarized light separating means side of the flat plate, for emitting the light from the light source to the first polarized light separating means side.
In this case, the uneven portion may contain a plurality of projections discretely provided.
Furthermore, in this case, the projections may have a size of 5 to 300 xcexcm.
In the embodiment comprising the light guide plate provided between the first polarized light separating means and the variable transmission polarization axis means, the light guide plate may exhibit substantially optical isotropy.
Alternatively, in the embodiment comprising the light guide plate provided between the first polarized light separating means and the variable transmission polarization axis means, the light guide plate may be optically uniaxial or biaxial.
In the embodiment comprising the light guide plate provided between the first polarized light separating means and the variable transmission polarization axis means, the first polarized light separating means may be adhered to the light guide plate with an adhesive.
In this case, the adhesive may also constitute the transmissive light diffusion layer. This construction permits the realization of a thin display device, and a decrease in the number of the parts.
In a display device in accordance with a further embodiment of the present invention, the variable transmission polarization axis means comprises a liquid crystal. Namely, the display device is constructed as a liquid crystal display.
In this case, the liquid crystal may be a TN liquid crystal, a STN liquid crystal, or a ECB liquid crystal. This construction enables high-quality bright image display to be realized relatively easily without positive-negative reversal between reflective display and transmissive display.
The object of the present invention can also be achieved by an electronic apparatus comprising the above-described display device of the present invention.
Since the electronic apparatus of the present invention comprises the display device of the above mentioned present invention, various electronic apparatus capable of displaying high-quality bright images can be realized.
The object of the present invention can also be achieved by a display device comprising a variable transmission polarization axis optical element; a first polarized light separator of a type in which polarized light separation is performed by reflection, and which is arranged on the one side of the variable transmission polarization axis optical element; a second polarized light separator of a type in which polarized light separation is performed by reflection or absorption, and which is arranged on the other side of the variable transmission polarization axis optical element; and a light source for making light incident from between the first and second polarized light separators.
In this display device, the first polarized light separator transmits a linearly-polarized light component which is in a first direction and emitted from the side of the variable transmission polarization axis optical element and reflects a linearly-polarized light component which is different from the first linearly-polarized light component, thereby separation of polarized light is performed. Therefore, the display device can obtain brighter display by utilizing the reflected linearly-polarized light component, as compared with a conventional display device using a polarizer for separating polarized light by absorption. Furthermore, in this display device, since light is incident between the first and second polarized light separators from the light source, the light is incident from the upper side of the first polarized light separator, thereby causing no positive-negative reversal. Also, freedom of the arrangement position of the light source, and design freedom of the display device are increased.